There are acknowledged health and nutritional benefits for humans in increasing the daily intake of soluble dietary fibres from oat and barley grains. In particular, the β-glucan component of these cereals has been related and directly linked to a number of beneficial effects, for example the demonstrated reduction of serum cholesterol levels, alongside improvements in HDL/LDL ratios in the blood, an effect strongly correlated with improved cardiovascular health in humans [Bell et al, Critical Reviews In Food Science and Nutrition, Vol 39, 2, 1999]. Additionally, highly viscous (and usually high molecular weight) non-starch polysaccharides present in whole cereal grains, may be implicated in mechanisms regulating blood glucose, with an implied beneficial effect in long term prevention of type 2 diabetes [Foster-Powell and Brand Miller, Am J. Clin. Nutr., 62, 871S-893S, 1995]. Of further significance, the soluble dietary fibres present in oat and barley are not digested in the human intestine and therefore pass through to the colon where they are available for microbial fermentation and as such are effective prebiotic materials.
Furthermore, the soluble β-glucans from oat and barley are very interesting as functional ingredients in foods as they exhibit gelling behaviour, stabilising properties, water binding and impart good mouth feel to products. High molecular weight β-glucans have potential as viscosity modifiers, colloidal stabilisers, texturisers etc in foodstuffs.
For many of the nutraceutical and Functional applications, it is crucial to maintain high molecular weights in the β-glucan component of the soluble fibre and to isolate the soluble fibre cost-effectively with a reasonably high concentration of β-glucan in the isolate. This “double challenge” is addressed in the present invention. Additionally, isolation of a reasonably clean fraction of soluble dietary fibre containing high molecular weight β-glucan at appreciable concentrations facilitates the cost-effective further processing of the material to yield preparations of very high β-glucan concentrations at high molecular weight, and to adjust molecular weight of the materials in a controlled manner to “tailor” final product properties. This issue is also addressed in the present invention. Finally, for soluble dietary fibres From oat and barley to impact significantly in the food markets, a process for their production must be cost effective and be capable of delivering materials at reasonable costs already accepted for food ingredients of various classes. The present invention also facilitates this.
Prior to the present invention, there exists no cost-effective process capable of, at the industrial scale, producing high molecular weight, concentrated preparations of soluble dietary fibre from oat and barley, which can be utilised directly as food ingredients. There is additionally no process, which can deliver β-glucan products of pre-determined molecular weight profiles, necessary to ensure correct function of the products in targeted end applications.
For example, inglett in two patent applications (U.S. Pat. No. 4,996,063 and WO 92/10106) describes methods to produce water-soluble dietary fibre compositions from milled, heat-treated oat flours and milled barley flours, via treatment with α-amylase enzymes to degrade starch components and subsequent centrifugation to remove insoluble materials from the hydrolysate mixture. The products are relatively low in soluble dietary fibre content, with no reference to the molecular weight of the β-glucan components. Only one enzyme type is utilised in the processes described. There is no description of a method to further enrich the β-glucan content of the material, or the separation of a distinct layer rich in high molecular weight β-glucan.
Lennart et al (U.S. Pat No. 5,686,123) inform on methods to produce soluble cereal suspensions from oat. The basis of the invention is treatment of previously heat-treated ground oat, with β-amylase class of enzyme, whilst slurried in water. A second α-amylase stage may be optionally included to further breakdown starch. No separation of a soluble dietary fibre rich component is described in the invention. The product slurry contains most of the protein and oil present in the raw material.
Triantafyllon, in WO 00/24270 describes a method to produce β-glucan soluble dietary fibre from heat-treated oat flour, using β-amylase enzyme to hydrolyse starch to lower molecular weight fragments, optionally including α-amylase and/or protease in a second stage hydrolysis, after which solids are centrifuged off, leaving a single soluble phase containing around up to 2% β-glucan before drying. There is no description or suggestion of the segregation of a fraction rich in soluble dietary fibre in this process, distinct from an aqueous syrup layer, and no product that can have a particularly high content of β-glucan is produced via the direct drying of the separated supernatant. The lack of a distinct separate viscous top layer on top of the bulk aqueous layer suggests there has been some degradation of β-glucans into smaller molecular weight fractions.
Indeed, most processes claiming to produce compositions containing high concentrations of soluble dietary fibres from oat and barley grain are based not on enzymatic extraction, but rather on alkaline extraction either from milled whole grain or a sleved fraction (Fisher et al, U.S. Pat No. 6,323,338), or even hot water extraction, which yields lower molecular weight soluble β-glucans (Roxdale Foods Ltd and Morgan; WO 02/02645 A1).
A precise methodology has now been discovered that addresses and solves the problems outlined above. The invention allows the cost-effective production of oat and barley soluble dietary fibre preparations containing β-glucans of high molecular weight, in concentrations of typically 20%-30%. The fraction containing the high molecular weight soluble dietary fibre component (20%-30% of dry matter) separates as a distinct viscous top layer during the process, above another distinct aqueous layer containing water soluble components. The fraction is relatively free of proteins and oils normally encountered during the processes described above. The clean fraction can then be separated very cost effectively from the other components and dries directly as a soluble white powder with negligible cereal taste. This of course greatly facilitates the further processing of this fraction containing the soluble dietary fibres with these characteristics and in these proportions, so that further enrichment (up to more than 60% β-glucan on a dry weight basis) becomes commercially and technically feasible. This is a major step forward in oat and barley processing.